2 clues have been given to you on post #7 and #11.

I'll give a simple example on how you can detect when there is current flow during charging. The values on the drawing may not work as you wanted as it only shows how I would do it just to trigger your imaginations.


LOAD1 is your output to your phone. Assuming a charging current of 200mA. R16 is a 2.2 Ω resistor connected in series with your load. It would drop 462mV so Q3 is conducting. This would make Q4 to conduct so the emitter of Q4 would be "High". You may use this logic level to control 555 whether to become flashong or not.

Since R16 drops about 0.5V from the 7805 regulator so D3 is added to make the output voltage of 7805 a diode drop higher ie 5.6V.

To control LM555 to flash or not. There are many ways to do it so I'll leave it to you to decide.

Allen

 

I'm still a novice when it comes to circuits; I'm only in year 10 (15 years old) so sorry if this sounds amateurish. Which IC pin would the arrow on top of R14 that says "to 555" connect to?

 

Sorry, I didn't know that you're so young and since your thread was in the "HomeWork Help", we're not supposed to give you the answer completely but just clues....

So here's the complete circuit. My first version used an AND gate (4081) between the output of 555 and Q2.


I also have another version using a comparator LM393. But that was superfluous....
HTH.

Allen

 

Sorry, I didn't know that you're so young and since your thread was in the "HomeWork Help", we're not supposed to give you the answer completely but just clues....

So here's the complete circuit. My first version used an AND gate (4081) between the output of 555 and Q2.
View attachment 130766

I also have another version using a comparator LM393. But that was superfluous....
HTH.

Allen

Thank you so much for the help. I understand and appreciate that I won't learn if people just give me the answer.

 

Sorry, I didn't know that you're so young and since your thread was in the "HomeWork Help", we're not supposed to give you the answer completely but just clues....

So here's the complete circuit. My first version used an AND gate (4081) between the output of 555 and Q2.
View attachment 130766

I also have another version using a comparator LM393. But that was superfluous....
HTH.

Allen

I had to change resistor 2.2 ohms to 4.7 ohms so that the voltage drop was 0.7V but now it works.

 

Good. At least you understand what is the purpose of R16 and you start to use OHM's law to calculate the value.

What if the current drops to 160mA. Would that be considered as charging is complete?

Allen

 

I rebuilt your circuit on circuit wizard and as aforementioned, it works fine. However, when I tried designing a crude PCB for it, it didn't seem to work. My suspicions were that pin 4 required the same voltage as pin 8, but on the schematic, pin 4 gets approximately 4.7V and it still works.
Here is my PCB layout:

The 9V battery represents the 12V solar cell I would be using and the off board resistor is the load/phone. Oh and I just realized that R7 10K is not connected to the transistor Q3, though even when I connected it, it still didn't work.

 

You need to review the schematic against what you have drawn in the above post.

 

I'll start with the BC557. What is the voltage across R4 ?

What are the voltage at E and C of BC557 ?

If you're getting 4.7V across R4, it means that Q3 is not conducting enough between C and E .

Allen

 

Did you refer to the datasheet of BC557and Bc108 for the printout?

Is your bc108 metal cased?

 

I rebuilt your circuit on circuit wizard and as aforementioned, it works fine. However, when I tried designing a crude PCB for it, it didn't seem to work.

My suspicions were that pin 4 required the same voltage as pin 8, but on the schematic, pin 4 gets approximately 4.7V and it still works.

I woke up this morning and tried my simulator with volt-meter added and I also saw that what you've suspected might be valid. Due to Q4 [in my schem] is in common collector mode, the gain is too low to reflect a voltage > 1/2 Vcc on the emitter.
So I changed it to common emitter mode and added another transistor Q5 to invert the signal.

Here's the new schematic

 

Have you reviewed this article on Lithium-ion battery charging?

It certainly has implications on your design.

 

Here is a simulation of absf's original design.

 

Thank you for simulating my original design and put it on video. That's the trick I have not learnt yet.

I admit that I didn't read the 555 datasheet thoroughly so I didn't know that the Reset can work at such a low voltage. Using multiple resistors with switches as the load was a plus and that simulate the situation more clearly and completely.

Let's wait what the TS has to say about this when he comes back. May be he needs more time to digest all these.

Allen

 

No problem. Im always trying to present material in a concise manner.

I did a transient stepped every 250 mS with the screen updated at the same time. I used a screen capture (video). I edited the screen capture to cut the excessive start and end using movie Maker. Saved that video and then created the movie you see above.

I purposely removed the values as this is the homework forum. I've done block diagrams from individual circuits as well.

 

Thanks for the help. I seemed to have fixed it myself by moving the 7805 Voltage Regulator right next to the supply voltage, so that it comes before the 555. This means the 555 pin 8 gets 5V and Pin 4 should get more or less the same.

 

If you required more than 1.1 volts to keep timer working properly, the reset circuitry wasn't working properly according to the datasheet.

What did you think of the video?